RobH

I've started a project that I've dubbed "Hover-Maxx". The project was partially inspired by an episode of Monster Garage where the team tried to make a Delorian into a hovercraft. Their project failed because the resulting craft was too heavy to be lifted by the blower.

Before I get started... No, I'm not going to make a T-Maxx hover. I'm using a pro-line T-Maxx body that will be the shell. It's a hummer body. The uncut, unpainted body measures 18 7/8 inches long and 7 inches wide. This is the measurement under the breadbox shaped cavity the uncut body makes.

I've purchased a sheet of 6061 aluminum (1/8th inch thick) and I've cut it to the above dimensions (little bigger).

The aluminum plate will have a rubber skirt around it. I'm having great success making a skirt out of a bicycle tube. I can cut the tube at 45 degree angles and sew it back together with upholstery thread. I'm still fine tuning the "shape" of the skirt, but when it's done, it will be a "square" bike inner-tube that is mitered on the corners. The test seems are sealed very very well. I originally wanted to use bicycle tube repair epoxy to seal the edges, but I might not even need that. The thread is also super strong and very impressive.

I've also cut out of the scrape aluminum pieces four strips of 6061. I've also mitered the four strips. When assembled they will make a "picture" frame that will bolt under the chassis. The skirt will have a 1-inch flap of rubber that be sandwiched between the strips of 6061 and the chassis (7x19ish aluminum plate). The edges of the aluminum strips will be ground and sanded so they don't rip the rubber inner tube.

I do have some pictures taken, but I don't have them with me right now.

So far the project is progressing well. My main concern at this point is "Hover Power". I need to lift a really heavy plate of aluminum plus two engines, four filled gas tanks (more on that later), 3 servos, a receiver and batteries. Not to mention other things like fans, fan housings, rudders and misc fabricated pieces. I'm guessing the beast is going to weigh around 10-12 pounds?

If I can push enough air down under the chassis, it will hover. The trick is over designing and having more HP (Hover Power) than you need. If you have too much power, it's easy to adjust the throttle on the blower engine. If you have too little, you just reenacted the Monster Garage episode in true scale fashion. (Does Anyone have a little army tank we can kill it with?)

I want to use one of my old .21 Buggy engines. It's "rated" at 2.7HP @ 38,000 RPM. That's way off the mark. I'd be surprised if it made 32,000 RPM. Anyway, the high RPM and HP (horsepower in this case) will surely be needed to get the beast off the ground.

The next kunundrum is a fan blade. I say fan blade, because props aren't nearly as good at pushing air. Can't I just stick a CPU fan on it? Hummm... no. Put some wussy fan on an engine that runs at 32,000 RPM and you just created a safety hazard. I touched on the idea of using a Ducted Fan Blade from the Nitro DF Jets. I finally ran down a Kress RK-720 fan blade. Some guy apparently attached these DF Units to NovaRossi .21 buggy engines and stuck them in Jets (sounds spot on). It's also only 3.5" in diameter. This is also good because my chassis is only 7" wide and I can't make a huge hole in it. It sounds like I found my blade.... NOT! Sadly, after all this research I realized that ducted fan blades don't "blow" or "push" air. Ducted Fan Jet fan blades "suck" or "pull" air towards the engine.

I want to mount my engine vertically with the shaft end facing the ground. If I were to use a Ducted Fan Blade from a Jet, it would suck it self to the ground in stead of blow air into the skirt. The world's most complicated suction cup!

I thought about inverting the engine and using the entire ducted fan unit. It would look something like the nose end of a turbine popping out the top of a hummer. If sounds cool and the parts are available, but the housing for the DF isn't long enough. My engine is huge compared to the DF unit. I'd have to slice a good chunk out of the housing to get the engine in there. Also, the duct wouldn't reach all the way down to the chassis. I'd have to fabricate a collar of sorts that would extend the duct down to the hole. Then you have the exhaust that would have to come out the side of the duct. And how do I mount my engine inside the duct? It's gets too complicated.

It would be much easier to just mount the engine with the shaft facing the ground. The only trick there is getting a fan blade that's 3-4 inches in diameter that "pushes" air. The kicker is the RPM thing. The fan has to be a beast.

I was thinking about the fan blades in electric (or even gas) leaf blowers. They can make 100 MPH winds, they have to be whipping that blade around pretty fast. Next question, how the hell do I mount a leaf blower fan blade to a Nitro engine? Would it even work?

At this point, I'm considering tanking the project.

Anyway, does anyone have any suggestions to get this thing off the ground? (literally)

The Key Factors:

10-12 lbs
7 inches wide by 18 7/8th inches long

-RobH

PS: Pics coming

hyper7

This project sounds pretty cool.
I see no problem with the ducted fan idea, all you have to do is reverse the fan it self this should only take its proformance down a little. An alternative idea is going with a prop. I have mounted both composite and wooden props on .16 engines with no problem. Props would be the best answer all you have to do is create a duct around the prop. (maybe pvc pipe). If your still unsure about propelors go out and buy one mount it to the engine and mount the engine on a piece of wood or in a vise and run it up to full throttle. I truly belive it will work

RobH

I thought I could swap the blan blade around (flip it over) and it would produce trust instead of suction.

I thought...

Look at the profile of over of these fan blades. In general, the blades start at the lower left and go up to the upper right. There is a bit of a "swoop" in there, but it's mostly bottom left to upper right. Now flip the fan blade over so what was the top is now the bottom. Take note of where the blade stops and starts. It's still starts at the bottom left and works it's way to the top right. The swoop now, however, it just tweaked in the oposite direction.

If you stop to think about it, a Nitro Engine should only run in one direction. If you're looking at the shaft end, it rotates counter-clock wise (at least mine do). Now put the blade on the engine and hold it to your chest with the shaft facing away. From, this perspective, the fan blades move left to right before they rotate down under the shaft.

Now you have to visualize the air moving through the fan blades. It's going to scoop the air that's the furthest away from you and bring it past the body of the engine and towards you. If you leave the engine in the same orientation and flip the fan blade over, the "scoop" part is now facing the wrong way. The blade in general, however, is still oriented so that it starts at the lower left and ends at the upper right. Because of this, it will still move air in the same direction! It just won't do as good of a job because the scoops are facing the wrong way.

It's a weird concept, but this is why airplane guys have normal props (blows air past and behind the engine) and pusher props (blows air away from the engine).

I need a "pusher" blade where ducted fan blades from RC Jets are "puller" blades.

I did give some thought to using a fat "pusher prop". I'm sure I can get it to make some air.

The problem, now, however is the density. I need to lift 10 pounds with a surface area of less than a square foot. I was checking out a table of weights on working hovercraft models. My engine is over kill. If I can make it push air, it might barely blow enough air to make it hover. A prop doing a fan's job is less efficient than a fan doing a fan's job. I believe that using a prop on my engine would result in a failed project because so much energy would be wasted because props are not optomized for moving air.

Anyway, I've tanked the project. I found the page on the RC hovercrafts and realized how silly the idea was just after I started this thread.

It would be cool to see a car body on a hovercraft. I think it would need to be made out of balsa wood and have to use electric motors though (you can run those backwards easy).

That type of stuff just isn't my bag. *shrug* Good luck if anyone else wants to try it.

-RobH

wyflyer

My Feedback: (7)

Delete